Polyester resins

ABSTRACT

Polyester imide resins containing 5-membered imide rings between the ester groups. The resins are soluble in cresol, and cresol solutions are useful as enameling lacquers for wire conductors.

United States Patent Schmidt et a1.

[ 1 Dec. 30, 1975 POLYESTER RESINS [76] Inventors: Karl Schmidt, Hofweg45;

Ferdinand Hansch, Kalenbarg 23; Hans-Malte Rombrecht, Overbeckstrasse 3;Hans-Joachim Beck, Am Langenzug 7, all of Hamburg, Germany 22 Filed:Oct. 2, 1972 21 App]. No.: 293,880

Related U.S. Application Data [60] Division of Ser. No. 659,234, Aug. 8,1967, Pat. No. 3,697,471, which is a continuation of Ser. No. 238,315,Nov. 2, 1962, abandoned.

[30] Foreign Application Priority Data Nov. 2, 1961 Germany 64660 Dec.12, 1961 Germany 65130 July 6, 1962 Germany 67934 [52] U.S. Cl. 260/33.4P; 260/33.6 R; 260/40 R; 260/75 N [51] Int. C13. C08G 73/16; C08K 5/01;C08K 5/13;

C08L 79/08 [58] Field of Search 260/37 N, 33.4 P, 78 TF, 260/75 N, 40 R[56] References Cited UNITED STATES PATENTS 2,421,024 5/1947 Frosch117/1284 2,710,853 6/1955 Edwards et a1 .1 260/78 3,060,191 10/1962 Kolbet a1. 260/78 TF 3,238,181 3/1966 Anderson 260/75 N 3,382,203 5/1968Rating et al. 1. 260/33.4 P

FOREIGN PATENTS OR APPLICATIONS 570,858 7/1945 United Kingdom 260/78 TFPrimary Examiner-Al1an Lieberman [57] ABSTRACT Polyester imide resinscontaining S-membered imide rings between the ester groups. The resinsare soluble in cresol, and cresol solutions are useful as enamelinglacquers for wire conductors.

6 Claims, No Drawings which is also a division of said Ser. No. 659,234and A claims certain of the compounds disclosed herein.

The present invention relates to polyester resins, and more particularlyto polyester resins which in addition to the ester groups also containimide groups, and also to a new series of imide group-containing agentswhich can be used to modify polyester resins.

Synthetic resins produced from polyvalent alcohols and polycarboxylicacids have been known for a long time. These are generally known underthe designation alkyd resins and provide one of the most importantclasses of synthetic resins. Alkyd resins have also been known to bemodified in various ways, primarily by the incorporation of natural orsynthetic fatty acids or their glycerides therein. The particularlytemperature stable alkyd resins are however the oil-free alkyd resins ofaromatic carboxylic acids, especially of isophthalic acid andterephthalic acid.

Alkyd resins have also been modified by the incorporation therein ofnitrogen-containing compounds, for example by the use therein ofdiamines, amino alcohols or amino carboxylic acids which are reactedwith the reactants used for forming the alkyd 'resins, or by thesubsequent reaction of the alkyd resins with polyisocyanates. Productsobtained in this manner exhibit improved elasticity and good temperaturestability. However. these resins also do not meet all of the necessaryrequirements for all applications.

For some time linear polyimide resins have been known, these having beenobtained by the condensation of diamines with tetracarboxylic acidanhydrides. These resins are makred by an extremely high softeningtemperature and duration of stability to high temperatures, as well asby a high stability against all normal solvents. This latter advantageactually makes it difficult to make use of an work up these linearpolyimide resins. Attempts have been made to avoid this advantage byfirst producing the linear polyimidocarboxylic acid which is onlysoluble in relatively expensive solvents and then thepolyimidocarboxylic acid after the fashioning thereof, for example as alacquer coating, fibers or the like. by heating or splitting off ofwater by means of suitable chemicals to subsequently convert the sameinto a polyimide. However, polyimidocarboxylic acids can only be madeinto lacquers in the form of solutions with a very low solid bodycontent, because concentrated solutions thereof possess too high aviscosity for working up. A further disadvantage of thepolyimidocarboxylic acids resides in the fact that the same cannot becontacted with iron, and consequently considerable apparatus expense inthe use of expensive noble metals is necessary in order to work with thesubstances.

It is accordingly a primary object of the present invention to provide anew series of resins which possess advantages not possessed by the abovementioned resins, and which consequently can be used for variousimportant technical purposes.

It is another object of the present invention to provide new polyesterimide resins ofsuperior characteristics.

It is yet another object of the present invention to provide. for themodification of polyester resins or alkyd resins of all types, andparticularly of alkyd resins produced from aromatic polycarboxylicacids, so as to improve the properties thereof.

It is another object of the present invention to provide a new series ofmodifying agents for the modification of polyester resins, thesemodifying agents being usable either during of after the production ofthe polyester resins.

It is still another object of the present invention to provide methodsof producing the new polyester imide resins of the present invention.

It is still another object of the present invention to provide lacquersof polyester imide resins for use in various applications, andparticularly for use as lacquers for the coating of magnetic wire andthe like electrical conductors.

It is still a further object of the present invention to provideinsulated electrical conductors which are insulated by means of thepolyester imide resins of the present invention.

Other objects and advantages of the present invention will be apparentfrom a further reading of the specifications and of the appended claims.

With the above and other objects in view, the present invention mainlycomprises the modifications of a polyester resin so that the samecontains at least one 5- member imide ring between functional groups ofthe molecule. Thus, in accordance with the present invention there isprovided ester imide resins, particulaly polyester resins of one or morepolycarboxylic acid and one or more polyvalent alcohol, as well ashydroxy carboxylic acids, and also as well as the use of thefunctionally active derivatives of the polycarboxylic acids and of thepolyvalent alcohols, in which one or more of the starting materialscontains one or more S-membered imide ring between the functional groupsof the molecule.

It has surprisingly been found that ester imide resins, which containnot only ester groups but also imide groups, on the one hand containmany properties which are better than those of the known alkyd resins,and on the other hand avoid the difficulties of the polyimide resins.This is accomplished by producing the ester imide resins ofpolycarboxylic acids, polyvalent alcohols, including hydroxy carboxylicacids or their derivatives, wherein one or more of the startingsubstances is partly or entirely of such compound that there is one ormore S-membered imide ring between the functional groups of themolecule.

Thus, for example, enameled lacquer films of the ester imide resins ofthe present invention posesses marked thermal stability, increasedsolvent resistance, hardness and flexibility. Particularly notable arethe improvements in the action of the combined mechanical and thermalstresses, such as in the thermal ageing of stretched or compressedlacquer films. Because of these advantageous properties, the products ofthe present invention are particularly suitable for the production ofenameling, particularly for magnetic wires for electrical insulationpurposes, since for these purposes materials possessing all of thesuperior properties of the products of the present invention were notknown, Thus, lacquer films of good resistance in the so-called heatshock test were unknown. Also of importance for the use of resins of thepresent invention as lacquers for magnetic wires or for electricalinsulation 3 purposes is the solubility thereof in cheap solvents suchas cresols, or if necessary in mixtures of cutting agents or diluents,such as solvent naphtha. In accordance with the present invention it ispossible to produce low viscosity lacquers of high solid body content.

It should also be noted that the ester imide resins of the presentinvention in the use thereof for enameling lacquers can be improved bythe addition of esters of titanic acid or of zirconic acid.

The combination of the advantageous properties of the polyimide resinsand of the polyester resins in the new polyester imide resins of thepresent invention could not be predicted, particularly with respect tothe suitable use thereof in the field of electrical insulation ofconductors such as copper wires. It is thus quite surprising that evenwith a slight content of imide groups the properties of the ester imideresins of the present inevention is markedly influenced. The use of theester imide resins of the present invention is, however, not limited toapplication for electrical insulation purposes. These resins can also beused for all other purposes for which the known alkyd resins could beused, particularly for all types of coatings, for the production offoils and films, and also for production of molded bodies.

As indicated above, the production of the ester imide resins accordingto the present invention is carried out by esterifying a polycarboxylicacid (or its functional derivatives) with a polyhydric alcohol as wellas with a hydroxy carboxylic acid, if desired, in known manner, wherebyin accordance with the present invention one or more of these startingsubstances contains between the functional groups in the molecule one ormore S-membered imide group. As is clear from the above instead of usingthe acids or alcohols themselves it is possible to use instead theirfunctional derivatives, such as their esters or semi-esters.

The imide group-containing starting materials of the desired structurewhich are used for the production of the ester imide resins of thepresent invention can, for example, be produced by reaction betweencompounds of the following two classes:-

a. An aromatic carboxylic acid anhydride which besides the S-memberedcyclic carboxylic acid anhydride group also contains at least oneadditional reactable group. These additional reactable groups can becarboxyl groups, an additional carboxylic acid anhydride group or ahydroxyl group.

In this class of compounds there can be used also, instead of the cycliccarboxylic acid anhydride groups, compounds in which two adjacent carbonatoms contain carboxyl groups, or to use esters of semi-or half esters,as well as their semi-or half imides with a primary amine of the typeset forth under (b) below. Any of these compounds of this type can beused for the imide formation.

b. A primary amine, which besides the primary amino group also containsat least one additional reactable group. These additional reactablegroups can be carboxyl groups, a hydroxyl group, or an additionalprimary amino group.

Instead of the primary amines it is possible to use their salts, amides,lactams or polyamides, so long as the bound primary amino group isreactable for imide formation.

Examples of compounds of a cyclic carboxylic acid anhydride grouping andan additional functional group falling under (a) above, and primarilypyromellitic acid anhydride and trimellitic acid anhydride. In additionother carboxylic acid anhydrides are suitable, such as naphthalenetetracarboxylic acid dianhydride or dianhydrides of tetracarboxylic acidwith two benzene nucleii in the molecule in which the carboxyl groups in3.3',4 4'-position.

Examples of compounds with a primary amino group and an additionalfunctional group falling under (b) above, are primarily the aliphaticdiprimary diamines such as ethylenediamine, tetramethylenediamine,hexamethylenediamine, nonoamethylenediamine, as well as aromaticdiprimary diamines such as benzidine, diaminodiphenylmethane,diaminodiphenylketone, diaminodiphenylsulfone, diaminodiphenylsulfoxide,diaminodiphenylether and diaminodiphenylthioether, phenylenediamine,toluylenediamine, xylylenediamine, as well as diamines with threebenzene nucleii in the molecule, such asbis-(4-aminophenyl)-a,ot'-p-xylol or bis-(4-aminophenoxy)-1,4-benzene,and also cycloaliphatic diamines, such as4,4'-dicyclohexylmethanediamine. Also suitable are amino alcohols suchas monoethanolamine, monopropanolamine or dimethylethanolamine, as wellas amino carboxylic acids such as glycocol, aminopropionic acids, aminocapronic acids or amino benzoic acids.

The reaction products of (a) and (b) above can be reacted with polyesterreactants, e.g. a polycarboxylic acid such as terephthalic acid and apolyhydric alcohol or alcohols such as ethylene glycol and/or glycerinto form the ester imide resins of the present invention, or thecompounds of (a) and (b) above can be reacted together with thepolyester-forming reactants, or a polyester may be reacted with thereaction product of (a) and (b) above or with the compounds of (a) and(b) above themselves. All of these methods of proceeding can be used toproduce the ester imide resins of the present invention, as will befurther detailed below.

It should be noted that throughout the specification and claims of thiscase whenever mention is made of a reactable group such as a carboxylgroup or the like it is possible to use not only the free functionalgroup itself, but to use its functionally active equivalent, e.g. theester, instead. Thus, for example, mention may be made of the reactionof terephthalic acid with a polyhydric alcohol to form the polyester. Itis apparent that instead of the terephthalic acid itself it is possible,and sometimes even desirable to use its functional equivalents such as alower dialkyl ester thereof, e.g. dimethyl terephthalate, diethylterephthalate of the like, or also to use a semi-or half ester such asmethyl terephthalate. The use of such functional equivalents which arein general well known in this art is meant to be comprehended within thescope of the present invention, and in this connection too, it should benoted that this discussion applied not only to the functionalderivatives of the carboxylic acids, but also of the amines, etc.

Among the most suitable imide group-containing starting materials forthe production of ester imide resins according to the present inventionare those obtained by the reaction of 2 mols of trimellitic acidanhydride (or its reactable derivatives or functional equivalents) with1 mol of a diprimary amine (or its reactable derivatives or functionalequivalents). The result of this reaction is a diamidodicarboxylic acidwhich may be used to form the ester imide resins of the presentinvention.

Likewise suitable is the monimidedicarboxylic acid obtained by thereaction of 1 mol of trimellitic acid anhydride with 1 mol of an aminocarboxylic acid.

A suitable diamidodicarboxylic acid for the production of ester imideresins of the present invention can be obtained by the reaction of 1 molof a tetracarboxylic acid dianhydride, such as pyromellitic aciddianhydride, with 2 mols of an amino carboxylic acid with primary aminogroups or their functional equivalents.

A particularly suitable diimide alcohol which can be used as an imidegroup-containing starting material for the production of the ester imideresins of the present invention may be obtained by reacting 1 mol of atetracarboxylic acid anhydride such as pyromellitic acid dianhydridewith 2 mols of an amino alcohol with primary amino groups.

A suitable monoimide hydroxy carboxylic acid which may be used accordingto the present invention may be obtained by the reaction of 1 mol oftrimellitic acid anhydride with 1 mol of an amino alcohol with primaryamino groups.

In general, for the formation of cyclic imide compounds it is desirablethat the used amount of the acid anhydride component (a) and of theamine component (b) are at least approximately equivalent.

As is clear from the above the imide group-containing starting materialcan be obtained by the reaction of an acid component (a) such astrimellitic acid anhydride and an amine component (b) such as adiprimary diamine of an amino carboxylic acid with primary amino groups,or instead of the trimellitie acid anhydride it is possible to use asthe acid component (a) a tetracarboxylic acid dianhydride such aspyromellitic acid dianhydride. Instead of the diprimary diamine or theamino carboxylic acid it is equally possible to use an amino alcoholwith primary amino groups.

It should also be noted that instead of using a single acid component ora single amine component for the formation of the imide group-containingstarting material it is possible, and sometimes even desirable, to use amixture of such components. Thus, for example, it is advantageous to useinstead of trimellitic acid anhydride itself, a mixture of trimelliticacid anhydride with up to 40% thereof substituted by an equivalentamount of pyromellitic acid anhydride. Likewise, it is possible tosubstitute, for example, up to of a monoalkanolamine with an equivalentamount of a diprimary amine which can either be an aliphatic, aromaticor aliphatic -aromatic diamine.

A particularly advantageous ester imide resin may be produced by thereaction of 1 mol of trimellitic acid anhydride with 0.35 0.8 mols ofmonoethanolamine and 0.2 2 mols of ethylene glycol. As indicated above,the trimellitic acid may be substituted in part by pyromellitic acid andthe monoethanolamine may be substituted in part by an equivalent amountof diprimary diamine. In addition, the ethylene glycol may besubstituted in part, for example up to about 0.4 mols thereof,calculated with respect to 1 mol of trimellitie acid anhydride, with anequivalent amount of a trihydric alcohol, or an alcohol with 4 or morehydroxyl groups.

The following examples A M relate to the production of imidegroup-containing starting materials for the production of ester imideresins according to the present invention. The scope of the inventionis, of course, not meant to be limited to these specific examples.

EXAMPLE A g (0.6 mols) of trimellitic acid anhydride are introduced into500 g of a technical cresol mixture at a temperature of C. When all ofthe trimellitic acid anhydride has been dissolved, 60 g (0.3 mol) of4,4- diaminodiphenyl methane are added thereto. This mixture is stirredfor 6 hours at 140C.

Upon cooling a yellowish, finely crystalline precipitate forms which isfiltered off and washed several times with alcohol and ether.

The obtained product does not melt at temperatures up to 360C.

EXAMPLE B 24.8 g (0.1 mol) of 4,4'-diaminodiphenyl sulfone and 38.4 g(0.2 mol) of trimellitic acid anhydride are stirred into 500 g oftechnical cresol mixture to form a slurry, and this slurry is heated for4 hours at C. After cooling there is obtained a white, crystallineprecipitate which is washed as described in Example A.

The product does not melt at temperatures up to 360C.

EXAM PLE C 32.4 g (0.3 mol) of p-phenylenediamine and 1 15.2 g (0.6 mol)of trimellitic acid anhydride are heated with 1200 g of technical cresolmixture for 4 hours at 180C. After cooling the mixture is filtered andthe green crystals constituting the obtained reaction product are washedas described in Example A.

The product does not melt at temperatures up to 360C.

EXAMPLE D 23.2 g (0.2 mol) of hexamethylenediamine and 76.8 g (0.4 mol)of trimellitic acid anhydride are heated for 3 hours at C. in 400 g ofatechnical cresol mixture. After cooling and filtering the obtained whitecrystals are washed with alcohol and ether.

The melting point of the product is 301C.

EXAMPLE E 20 g (0.1 mol) of 4,4-diaminodiphenyl ether and 38.4 g (0.2mol) of trimellitic acid anhydride are heated for 4 hours at 200C. and500 g of technical cresol mixture, whereby a portion of the cresol isdistilled off. After cooling and filtering the obtained brown crystalsare washed with alcohol and ether.

The product does not melt at below 360C.

EXAMPLE F 334 g (2.44 mol) of p-aminobenzoic acid are dissolved in 1700cc of warm technical cresol mixture. This solution is added to a warmsolution of 446 g (2.44 mol) of trimellitic acid anhydride in 1300 g oftechnical cresol. These conbined solutions are then heated to refluxingfor 1 hour. After cooling and filtering the very finely granular whitepowder is washed with alcohol and ether. 7

The product does not melt at below 360C.

Titration of the acid in dimethyl formamide with water free sodiummethylate solution with cresol red as indicated gives an equivalentweight of 153 (calculated value 155.5).

EXAMPLE 75 g (1 mol) of glycocol and 500 cc of technical cresol areheated to 100C. To the obtained suspension is added in small portions109 g (0.5 mol) of pyromellitic acid anhydride. The mixture is thenfurther heated to 200C., whereby water distills off. After cooling thefinely crystalline residue is filtered off and washed with methylenechloride. After recrystallization from 1,4- dioxane the product which isobtained is in the form of yellowish-white crystals and does not melt upto temperatures of 320C.

EXAMPLE H 334 g (2.44 mol) of p-aminobenzoic acid is dissolved underwarming in 1300 cc of technical cresol mixture and the solution is addedto a hot solution of 266 g (1.22 mol) of pyromellitic acid dianhydridein 800 cc of cresol. The mixture is heated for hours at 190C., whereby50 cc of water distilled off. The precipitated white precipitate isfiltered off after cooling and washed with methanol and water.

EXAMPLE .1

EXAMPLE K 218 g (1 mol) of pyromellitic acid anhydride are dissolved in400 cc of dimethyl formamide at 80C. under nitrogen atmosphere.Monoethanolamine is slowly added dropwise to this solution at the sametemperature in an amount of 122 g (2 mol). The dimethyl formamide issubsequently distilled off under vacuum at a temperature between 100 and120C. The dirty white residue is recrystallized with the addition ofactivated carbon from 1,4-dioxane, whereby finely yellowish-whitecrystals having a melting point of 271C. are obtained.

EXAMPLE L 218 g (1 mol) of pyromellitic acid dianhydride and 150 g (2mol) of 3-aminopropanol are mixed with each other as described inExample H. The obtained crude product is recrystallized from ethyleneglycol monomethyl other with the addition of activated carbon. Theobtained white crystalline powder melts at 234C.

EXAMPLE M 192 g (1 mol) of trimellitic acid anhydride are dissolvedunder nitrogen atmosphere at 100C. in dimethyl formamide and there isadded dropwise to the solution at 60C. 61 g (1.0 mol) ofmonoethanolamine. The solvent is subsequently distilled off under vacuumat temperatures of 100 130C. The yellowish-white residue isrecrystallized two times from dioxane with the addition of activatedcarbon. and the compound melts at 197C.

Instead of producing the imide group-containing compounds as describedin the previous examples, to isolate the same and then to use them asstarting compounds for the production of the ester imide resinsaccording to the present invention, it is also possible, as indicatedpreviously, to produce the imide group-containing compounds during thesynthesis of the ester imide resins and to directly react the same withthe polyester reactants. Essentially the same type of ester imide resinsare obtained if the imide group-containing compounds are not firstseparately produced and isolated, but instead the compounds (a) and (b)are permitted to react in the apparatus used for the production of theester imide resin and then directly permitted to react with the otherstarting materials used in the production of the ester imide resin.

The point of time at which the compounds (a) and (b) are brought toreaction is not essential. In many cases it is preferable to firstproduce the imide groupcontaining compounds by reacting (a) and (b) andthen to use the resulting compound in the further production of theester imide resin by adding this compound to the esterificationreactants. It is also possible, however, to first esterify the imidegroup-free starting substances with each other, then to add the reactionproduct of compounds (a) and (b) thereto and to react these together andsubsequently to cause the resulting imide group-containing compound toreact with the already formed polyester resin. On the other hand it isalso possible and sometimes advantageous to mix the compounds (a) and(b) with the other starting materials used for the production of theester imide resins together and then to react all of the componentstogether.

The following examples are given to illustrate the production andworking up of the ester imide resins of the present invention. The scopeof the invention is not, however, meant to be limited to the specificdetails of these examples.

EXAMPLE 1 A polyester is produced in known manner from 388 g of dimethylterephthalate, 112 g of ethylene glycol and g of glycerin and thispolyester is mixed in two portions with 137 g of the reaction product ofExample A at a temperature of 215C. After the diimidedicarboxylic acid(reaction product Example A) has been completely taken up in theterephthalic acid resin, 1.8 g of cadmium acetate is added thereto. Thereaction mixture is subsequently further condensed for 3 hours at 215C.,finally under vacuum. The thus obtained resin is dissolved in 450 g oftechnical cresol while still hot and this solution is reacted with asolution of 9 g of butyl titanate in g of cresol.

The resulting lacquer is then diluted with a mixture of 2 parts ofsolvent naphtha and 1 part of cresol to a solid body content of 37% andthe resulting lacquer has a viscosity according to DlN 53 21 1 with a 4mm nozzle at 20C. of 156 seconds. (The expression D1N" stands forDeutsche lndustrienormalien which is the German Industrial Standards.

Copper Wire of 1 mm diameter is lacquered in a continuous process withthis wire lacquer in accordance with the following technical data:Horizontal wire lacquering oven of 3.50 meters length, oven temperature470C, coating apparatus of rollers and felt, 6 coats, drawing speed of 4m/min., coating thickness increase of diameter of the wire) 0.05 mm.

9 The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 H lead pencil hardness after 30 minutes storage at60C. in alcohol 3 H heat shock test: a winding of the wire around itsown diameter is unobjectionable after 1 hour of heating at a temperatureof 155C.

After 24 hours of ageing at 180C. the lacquer elongation amounts to 34%.The insulation is and remains solid upon winding about its own diameterunder a tension load of 0.6 kp/mm (kp kilopond).

EXAMPLE 2 A polyester is produced in known manner from 388 g of dimethylterephthalate, 112 g of ethylene glycol and 75 g of glycerin, and mixedwith 204 g of the reaction product of Example A at a temperature of 180215C., in two portions. After the diimidodicarboxylic acid (of ExampleA) is completely taken up in the terephthalate resin, 1.0 g of cadmiumacetate is added thereto and the reaction mixture is further condensedfor 3 hours at 215C., finally under vacuum. The ob.- tained resin isdissolved in 450 g of technical cresol while still hot, and mixed with asolution of 9 g of butyl titanate in 27 g of cresol.

This lacquer is diluted to a solid body content of 34% and a viscosityof 120 seconds as described in Example 1, and copper wire is lacqueredtherewith.

The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 H lead pencil hardness after 30 minutes storage at60C. in alcohol 3 H heat shock test: a winding of the wire on its owndiameter remains free of faults al'ter l hour heating at 155C.

After 16 hours of ageing at 200C. the elongation of the lacquer is 22%.The insulation remains solid upon winding about 4 times its own diameterunder a tension load of 6 kp/mm EXAMPLE 3 A polyester is produced inknown manner from 388 g of dimethyl terephthalate, 112 g of ethyleneglycol and 75 g of glycerin, and mixed with 273 g of the reactionproduct of Example A, added thereto in two portions at a temperatue of180 215C. Subsequently the reaction product is worked up as described inExample 1, the obtained lacquer is diluted to a solid body content of27% and the viscosity of 55 seconds, and copper wire is lacqueredtherewith.

The testing of the insulation of the lacquer gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 2 3 H lead pencil hardness altcr 30 minutes storageat 60Cv in alcohol 2 3 H 10 heat shock test: A winding of the wire aboutits own diameter of the wire prestretched 10% is free of faults about 1hour of tempering at 155C.

After 24 hours of ageing at 180C. the elongation of the lacquer amountsto 30%. The insulation remains solid upon winding about its own diameterunder a tension load of 0.6 kg/mm EXAMPLE 4 A polyester produced inknown manner from 388 g of dimethyl terephthalate, 1 12 g of ethyleneglycol and g of glycerin has g of technical cresol added thereto and themixture is heated to 80C. 144 g of trimellitic acid anhydride and 74 gof 4,4- diaminodiphenyl methane is then added to the resin melt and thetemperature is slowly increased to 215C. At C. the resin melt becomesturbid and highly viscous, obviously due to the formation and separationof the diimidodicarboxylic acid of Example A.

Upon further temperature increase the reaction mixture slowly becomesthinly liquid again and the precipitated diimidodicarboxylic acid isgradually taken up by the resin melt. After the resin melt reaches atemperature of 215C. it becomes clear, then 1 g of cadmium acetate isadded thereto and the cresol is distilled off under vacuum at C. Thereaction mixture is further condensed finally for an additional 3 hoursat 215C. The obtained resin is further worked up according to Example 1to a lacquer of 34% solid body content and the viscosity of 108 seconds,and a copper wire is then enameled therewith.

The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 H lead pencil hardness after 30 minutes storage at60C. in alcohol 3 H heat shock test: a winding of the wire about its owndiameter is free of faults after 1 hour of tempering at 155C.

After 16 hours storage at 200C. the elongation of the lacquer amounts to23%. The insulation is solid upon winding about 4 times its own diameterunder a tension load of 6 kp/mm".

EXAMPLE 5 388 g of dimethyl terephthalate, 112 g of ethylene glycol, 75g of glycerin, 150 g of technical cresol mixture, 144 g of trimelliticacid anhydride and 74 g of 4,4'-diaminodiphenyl methane are meltedtogether with the addition of 1 g of cerium naphthenate and stirredwhile heating. At about 130C. the separation of the diimidodicarboxylicacid described in Example 1 starts. Upon further slow temperatureincrease methanol and water distill off. Upon reaching a temperature of215C. the temperature is maintained for 3 hours and the resulting resinmelt becomes clear. 1 g of cadmium acetate is added thereto, the cresolis distilled off under vacuum at a temperature of C., and finallycondensation is continued for an additional 3 hours at 225C.

The obtained resin is worked up as described in EX- ample l to a lacquerof 34% solid body content and a viscosity of 120 seconds. and copperwire is enameled therewith.

1 1 The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 H lead pencil hardness after 30 minutes storage at60C. in alcohol 2 H heat shock test: A winding of the wire about its owndiameter is free of faults after tempering for 1 hour at 155C.

EXAMPLE 6 144 g of trimellitic acid anhydride, 74 g of 4,4-diaminodiphenyl methane, and 500 g of technical cresol are heated undervigorous stirring, whereby the resulting suspension at 150C. becomeshighly viscous. Upon further temperature increase to 195C. 27 cc ofwater distills off. Subsequently 200 cc of cresol distills off at 120C.under vacuum.

To the suspension of diimidodicarboxylic acid resulting therefrom isadded 388 g of dimethyl terephthalate, l 12 g of ethylene glycol and 75g of glycerin along with l g of cerium naphthenate. The mixture isheated, whereupon methanol and water distill off. The temperature isthen increased to 215C. and maintained at this temperature until theresin melt becomes clear. After the addition of 1 g of cadmium acetatethe remaining cresol is distilled off under vacuum at 170C. and theresin melt is further condensed an additional 3 hours at 215C.

The remaining resin is further worked up as described in Example 1 to alacquer of 34% solid body content and a viscosity of 1 12 seconds, andcopper wire is lacquered therewith.

The testing of the lacquer insulation gives the following values:

lead pencil hardness lead pencil hardness after 30 minutes storage at60C. in benzene 3 H lead pencil hardness after 30 minutes storage at60C. in alcohol 3 H A winding of the wire about its own diameter is freeof faults after 1 hour of tempering at 155C.

heat shock test:

After 16 hours of ageing at 200C. the lacquer elongation amounts to 24%.

The insulation remains solid upon winding about 4 times its own diameterunder a tension load of 6 kp/mm EXAMPLE 7 12 until the resin becomesclear. After the addition of 350 g of technical cresol the mixture iscooled to C.

Thereupon 299 g of trimellitic acid anhydride and 154 g of4.4'-diaminodiphenylmethane are again added and the mixture is furtheresterified at 215C. until a clear resin melt is obtained. The obtainedproduct is dissolved in 1 g of cresol and 600 g of solvent naphtha andthe mixture of 20 g of butyl titanate and 60 g of cresol are added tothis solution.

This solution is diluted to a solid body content of 27% and a viscosityof 123 seconds as described in Example 1 and copper wire is lacqueredtherewith.

The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 H lead pencil hardness after 30 minutes storage at60C. in alcohol 3 H A winding of the wire about itsown temperatureremains free of faults after 1 hour of tempering at 200C.

heat shock test:

EXAMPLE 8 218 g of diimidodicarboxylic acid produced according toExample A, 13 g of trimellitic acid anhydride, 31 g of ethylene glycol,12 g of glycerin and 1 g of tin (ll) oxalate in 500 g of technicalcresol for 8 hours at 185C. 225 g of cresol are then distilled off andthe residue is heated for an additional 8 hours at 200C. The obtainedresin solution is diluted to a lacquer of 27% solid body content and theviscosity of seconds as described in Example 1 and copper wire islacquered therewith.

The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 4 H lead pencil hardness after 30 minutes storageat 60C. in alcohol 3 4 H heat shock test: A winding of the wire aboutits own diameter is free of faults after 1 hour of tempering at 250C.

EXAMPLE 9 546 g of diimidodicarboxylic acid of Example A, 43.5 g ofethylene glycol and 43.5 g of glycerin, as well as 2 g of tin (ll)oxalate and 2 g of antimony (lll) oxide are heated in 1000 g of o-cresolfor 8 hours at C., whereby the reaction water is distilled off.Subsequently 740 g of cresol are distilled off and the residue is heatedfor 6 hours at 200C. The obtained resin solution is diluted as describedin Example 1 to a lacquer of 29% solid body content and a viscosity of123 seconds, and copper wire is lacquered therewith.

1 3 The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 4 H lead pencil hardness after 30 minutes storageat 60C. in alcohol 3 4 H heat shock test: A winding of the wire aboutits own diameter is free of faults after 1 hour of tempering at 250C.

After 16 hours of ageing at 200C. the lacquer elongation amounts to 33%.The insulation is solid upon winding about 4 times its own diameterunder a tension load of 6 kp/mm' EXAMPLE 10 The procedure followed is asdescribed in Example 2 with the exception that instead of 204 g of thediimidodicarboxylic acid of Example A, there is used 171 g of thediimidodicarboxylic acid of Example D. The obtained lacquer has a solidbody content of 34% and a viscosity of 110 seconds. Copper wire islacquered therewith.

The testing of the lacquer insulation gives the follow ing values:

lead pencil hardness 3 H lead pencil hardness after 30 minutes storageat 60C. in benzene 2 H lead pencil hardness after 30 minutes storage at60C. in alcohol 2 H heat shock test: A winding of the wire about its owndiameter remains free of faults after 1 hour heating at 155C. A windingof the wire about 2 times its own diameter remains free of faults afterl hour of tempering at 200C.

After 16 hours of ageing at 200C. the lacquer elongation amounts to 23%.The insulation remains solid upon winding about 4 times its own diameterunder a tension load of 6 kp/mm EXAMPLE 1 l lead pencil hardness 4 Hlead pencil hardness after 30 minutes storage at 60C. in benzene 3 Hlead pencil hardness after 30 minutes storage at 60C. in alcohol 3 Hheat shock test: A winding of the wire prestretched 10% about its owndiameter remains free of faults after 1 hour of tempering at After 24hours of ageing at 180C. the lacquer elongation amounts to 32%. Theinsulation remains solid upon winding about its own diameter under atension load of 0.6 kp/mm EXAMPLE 12 A polyester is produced in knownmanner from 388 g of dimethyl terephthalate, 112 g of ethylene glycoland g of glycerin are further worked up as described in Example 1.However, instead of the 137 g of diimidodicarboxylic acid of Example Athere is used g of the reaction product of Example G. The obtainedlacquer has a solid body content of 33% and a viscosity of 1 11 secondsand copper wire is lacquered therewith as described in Example 1.

The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 4 H lead pencil hardness after 30 minutes storageat 60C. in alcohol 3 4 H heat shock test: A winding of the wire aboutits own diameter remains free of faults after 1 hour of tempering at C.

After 16 hours of ageing at 200C. the insulation remains solid uponwinding about 4 times its own diameter under a tension load of 6 kp/mmEXAMPLE 13 218 g of dimethyl terephthalate, 28 g of ethylene glycol, 46g of glycerin and 102 g of the reaction product of Example K, with theaddition of 1. g of cerium naphthenate and 0.4 g of cadmium acetate, areesteritied for 12 hours. During this period the temperature is graduallyincreased from C. to 240C. As a result the methanol bound to thedimethyl terephthalate distills off. After the end of the reaction theresin is dissolved in a mixture of 285 g of technical cresol and l 85 gof solvent naphtha and stirred with 23 g of a 15% solution of butyltitanate in a cresol-solvent naphtha mixture.

The obtained lacquer of 30% solid content and a viscosity of 92 secondsis used for the lacquering of copper wire as in Example 1.

The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 4 H lead pencil hardness after 30 minutes storageat 60C. in alcohol 3 4 H heat shock test: A winding of the wireprestretched 10% about its own diameter is free of faults after l hourof tempering at 155C.

After 24 hours of ageing at 180C. the lacquer elongation amounts to 31%.The insulation is solid upon winding about its own diameter under atension load of 0.6 kp/mm".

EXAMPLE 14 218 g of dimethyl terephthalate, 28 g of ethylene glycol, 46g of glycerin and l l l g of the reaction product of Example L, with theaddition of l g of cerium naphthenate and 0.4 g of cadmium acetate aremixed with each other and reacted as described in Example 12. Theobtained lacquer of 26% solid body content and a viscosity of 130seconds is used for the lacqering of copper wire as described in Example1.

The testing of the lacquer insulation gives the following values:

lead pencil hardness 3 H lead pencil hardness after 30 minutes storageat 60C. in benzene 2 H lead pencil hardness after 30 minutes storage at60C. in alcohol 2 H heat shock test: A winding of the wire about its owndiameter remains free of faults after 1 hour tempering at 155C.

After 16 hours of ageing at 200C. the lacquer elongation amounts to 22%.The insulation is solid upon winding about 4 times its own diameterunder a tension load of 6 kp/mm EXAMPLE 15 A polyester is produced from300 g of dimethyl terephthalate, 64 g of ethylene glycol and 63 g ofglycerin under the addition of 65 g of technical cresol, and 248 g ofthe reaction product of Example M are added at 125C. The temperature of190- 220C. is used for esteriflcation until an acid number of less than10 is obtained. The reaction mass is subsequently further condensed anadditional 90 minutes at 190 230C. with the distillation off of cresolunder vacuum.

The resulting resin melt is mixed while still hot with 450 g oftechnical cresol and there is subsequently added a mixture of l 1 g ofbutyl titanate, 17 g of cresol and 17 g of solvent naphtha andthereafter it is diluted with a mixture of equal parts of cresol andsolvent naphtha to a solid body content of 25% and a viscosity of 111seconds.

The copper wire of 1 mm diameter is lacquered with this lacquer asdescribed in Example 1.

The testing of the lacquer insulation gives the following values:

heat shock test: A winding of the wire about its own diameter remainsfree of faults after l hour of tempering at 155C.

EXAMPLE 16 40 g of monoethanolamine are added dropwise to a mixture of192 g of trimellitic acid anhydride and 500 g of technical cresol at atemperature of C. under stirring, and then 450 g of cresol are againdistilled off at 130C. under vacuum. 65 g of ethylene glycol are thenadded and the mixture is esterified at a temperature of 160- 200C. witha distillation off of water until the reaction product has an acidnumber of 3. Subsequently during a two hour time period an additional 50g of distillate are distilled off under vacuum at a temperature of 210C.

The residue is dissolved hot in a mixture of 450 g of cresol and 150 gof solvent naphtha and the thus obtained solution has a solid bodycontent of 27% and a viscosity of 135 seconds.

Copper wire of 1 mm diameter is lacquered with this solution using ahorizontal lacquering oven of 2.5 m length and an oven temperature of500C. The drawing speed amounts to 2.3 m/min. Six coatings are applied,whereupon a diameter increase of the wire of 0.045 mm is obtained.

The testing of the lacquer insulation gives the following values:

A winding of the wire about its own diameter is free of faults after 1hour of tempering at 155C.

heat shock test:

After 16 hours of ageing at 200C. the insulation is solid upon windingabout 4 times its own diameter under a tension load of 6 kplmm EXAMPLE17 l 16 g of trimellitic acid anhydride and 65 g of pyromellitic aciddianhydride are dissolved in 200 g of dimethyl formamide at atemperature of C. and 43 g of monomethanolamine are added dropwise understirring to the solution of 60C. 185 g of dimethyl formamide aresubsequently distilled off under vacuum at C. After the addition of 56 gof ethylene glycol the reaction mixture is esterified 7 hours at atemperature from 170C. gradually increasing to 220C. whereby anadditional 20 g of distillate are obtained.

The obtained resin is dissolved hot in a mixture of 380 g of technicalcresol mixture and 130 g of solvent naphtha. The obtained lacquer has asolid body content of 38% and a viscosity of 149 seconds and is used forthe lacquering of copper wire as described in Example 16.

The testing of the lacquer insulation gives the following values:

heat shock test: A winding in the wire about its own diameter is free offaults after 1 hour tempering at C.

EXAMPLE 18 192 g of trimellitic acid anhydride are dissolved in 200 g ofdimethyl formamide at 90C. and 30 g of 4,4-diaminodiphenylmethane areadded in small portions to the solution at 60C., whereby a lightyellowish precipitate gradually precipitates. 28 g of monoethanolamineare subsequently added dropwise and g of dimethyl formamide are againdistilled off under vacuum at a temperature of 140C. The residue isesterified with 64 g of ethylene glycol for 6 hours, whereby thetemperature during this time is gradually increased, 170C. to 220C. 25 gof distillate are thus obtained, and upon a subsequent vacuum treatmentfor 90 minutes at 220C. an additional 25 g of distillate are obtained.

The residue is dissolved still hot in a mixture of 425 g of technicalcresol and g of solvent naphtha. The obtained lacquer has a solid bodycontent of 33% and 17 a viscosity of 1 18 seconds and is used for thelacquering of copper wires described in Example 16.

The testing of the lacquer insulation gives the following values:

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 H lead pencil hardness after 30 minutes storage at60C. in alcohol 3 H heat shock test: A winding of the wire about its owndiameter is free of faults after tempering for 1 hour at 200C.

EXAMPLE 19 A mixture of 192 g of trimellitic acid anhydride and 200 g ofdimethyl formamide are heated to 100C. under stirring, whereby a clearsolution results. 34 g of monoethanolamine are added thereto at 80C.dropwise and subsequently the dimethyl formamide is distilled off at 100150C. under vacuum. 52 g of neopentyl glycol and 53 g of ethylene glycolare then added thereto and the temperature is increased gradually andevenly from 180C. during a time period of 9 hours to 220C. with aseparation of 30 g of distillate, the esteritication being carried outuntil an acid number of 6 is obtained. The reaction mixture is thenfurther condensed for 2 hours at 220C. under vacuum.

The obtained resin is dissolved hot in a mixture of 500 g of technicalcresol and 250 g of solvent naphtha. The lacquer has a solid bodycontent of 28% and a viscosity of 135 seconds. The lacquer is used forthe lacquering of copper wire as described in Example 16.

lead pencil hardness 4 H lead pencil hardness after 30 minutes storageat 60C. in benzene 3 H lead pencil hardness after 30 minutes storage at60C. in alcohol 3 H heat shock test: A winding of the wire about its owndiameter remains free of faults after l hour of tempering at 155C.

EXAMPLE In accordance with the method described in Example 16 a resin isproduced of the following starting components: 192 g of trimelliticacid, 37 g of ethylene glycol, 18 g of glycerin and 43 g ofmonoethanolamine. The obtained brown resin is dissolved hot in a mixtureof 290 g of cresol and 90 g of solvent naphtha and the mixture is thendiluted with a mixture of equal parts of cresol and solvent naphtha to asolid body content of 27% and a viscosity of 119 seconds. This lacqueris then used for the lacquering of copper wire as described in Example16.

LII

The testing of the lacquer insulation gives the follow- -eontinued heatshock test: A winding of the wire about its own diameter remains free offaults after 1 hour of tempering at C.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A lacquer comprising a polyester imide resin dissolved in an organicmedium containing as an essential component thereof a cresol typesolvent, said polyester imide resin having ester groups of acid andalcohol moieties which are condensation products of at leastdifunctional carboxylic acid and at least difunctional alcohol, and,between said moeities, moieties containing a S-membered imide ring andwhich are condensation products of 1 mol of trimellitic acid anhydrideand 1 mol of primary aromatic amino earboxylic acid or primary aromaticamino alcohol, said moieties containing a S-membered imide ring beingpresent in an amount effective to improve the thermal stability of theresin without rendering the resin insoluble to an extent which wouldmake it unsuitable for use in a wire lacquer composed of the resindissolved in cresol and solvent naphtha.

2. A lacquer according to claim 1, said moieties containing a S-memberedimide ring being the condensation product of 1 mol of trimellitic acidanhydride and 1 mol of primary aromatic amino carboxylic acid.

3. A lacquer according to claim 1, said moieties containing a S-memberedimide ring being the condensation product of 1 mol of trimellitic acidanhydride and 1 mol of primary aromatic amino alcohol.

4. A lacquer comprising a polyester imide resin dissolved in an organicmedium containing as an essential component thereof a cresol typesolvent, said polyester imide resin having ester groups of acid andalcohol moieties which are condensation products of at leastdifunctional carboxylic acid and at least difunctional alcohol, and,between said moieties, moieties containing a S-membered imide ring andwhich are condensation products of 1 mol of tetracarboxylic acidanhydride and 2 mols of primary aromatic amino carboxylic acid orprimary aromatic amino alcohol, said moieties containing a 5 -memberedimide ring being present in an amount effective to improve the thermalstability of the resin without rendering the resin insoluble to anextent which would make it unsuitable for use in a wire lacquer composedof the resin dissolved in cresol and solvent naphtha.

5. A lacquer according to claim 4, said moieties containing a S-memberedimide ring being the condensation product of 1 mol of tetracarboxylicacid anhydride and 2 mols of primary aromatic amino carboxylic acid.

6. A lacquer according to claim 4, said moieties containing a S-memberedimide ring being the condensation product of 1 mol of tetracarboxylicacid anhydride and 2 mols of primary aromatic amino alcohol.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,929,714 DATED December 30, 1975 INVENTOR(S) 1 Karl Schmidt,Ferdinand Hansch and Hans-Malta It is certified that error appears inthe above-identified patent and that said Lette g rfi are herebycorrected as shown below:

Col. 4, line 5, after "groups" insert --are-;

line 55, change "applied" to -applies--;

line 67, change "monimide. to --monoimide.

' Signed and Sealed this Fifth D of 1m 1979 [SEAL] A Arresr:

RUTH C MASON DONALD W. BANNER Arresting Oflieer Commissioner of Parentsand Trademarks

1. A LACQUER COMPRISING A POLYESTER IMIDE RESIN DISSOLVED IN AN ORGANICMEDIUM CONTAINING AS AN ESSENTIAL COMPONENT THEREOF A CRESCOL TYPESOLVENT, SAID POLYESTER IMIDE RESIN HAVING ESTER GROUPS OF ACID ANDALCOHOL MOIETIES WHICH ARE CONDENSATION PRODUCTS OF AT LAST DIFUNCTIONALCARBOXYLIC ACID AND AT LEAST DIFUNCTION ALCOHOL, AND BETWEEN SAIDMOIETIES, MOIETIES CONTAINING A 5-MEMBERED IMIDE RING AND WHICH ARECONDENSATION PRODUCTS OF 1 MOL OF TRIMELLITIC ACID ANHYDRIDE AND 1 MOLOF PRIMARY AROMATIC AMINO CARBOXYLIC ACID OR PRIMARY AROMATIC AMINOALCOHOL, SAID MOIETIES CONTAINING A 5-MEMBERED IMIDE RING BEING PRESENTIN AN AMOUNT EFFECTIVE TO IMPROVE THE THERMAL STABILITY OF THE RESINWITHOUT RENDERING THE RESIN INSOLUBLE TO AN EXTENT WHICH WOULD MAKE ITUNSUITABLE FOR USE IN A WIRE LACQUER COMPOSED OF THE RESIN DISSOLVED INCRESCOL AND SOLVENT NAPTHA.
 2. A lacquer according to claim 1, saidmoieties containing a 5-membered imide ring being the condensationproduct of 1 mol of trimellitic acid anhydride and 1 mol of primaryaromatic amino carboxylic acid.
 3. A lacquer according to claim 1, saidmoieties containing a 5-membered imide ring being the condensationproduct of 1 mol of trimellitic acid anhydride and 1 mol of primaryaromatic amino alcohol.
 4. A LACQUER COMPRISING A POLYESTER IMIDE RESINDISSOLVED IN AN ORGANIC MEDIUM CONTAINING AN ESSENTIAL COMPONENT THREOFA CRESCOL TYPE SOLVENT, SAID POLYESTER IMIDE RESIN HAVING ESTER GROUPSOF ACID AND ALCOHOL MOIETIES WHICH ARE CONDENSATION PRODUCTS OF AT LASTDIFUNCTIONAL CARBOXYLYIC ACID AND AT LEAST DIFUNCTIONAL ALCOHOL, ANDBETWEEN SAID MOIETIES, MOIETIES CONTAINING A 5-MEMBERED IMIDE RING ANDWHICH ARE CONDENSATION PRODUCTS OF 1 MOL OF TETRACARBOXYLIC ACID OR AND2 MOLS OF PRIMARY AROMATIC AMINO CARBOXYLIC ACID OR PRIMARY AROMATICAMINO ALCOHOL SAID MOIETIES CONTAINING A 5 MEMBERED IMIDE RING BEINGPRESENT IN AN AMOUNT EFFECTIVE TO IMPROVE THE THERMAL STABILITY OF THERESIN WITHOUT RENDERING THE RESIN INSOLUBLE TO AN EXTEND WHICH WOULDMAKE IT UNSUITABLE FOR USE IN A WIRE LACQUER COMPOSED OF THE RESINDISSOLVED IN CRESCOL AND SOLVENT NAPHTHA.
 5. A lacquer according toclaim 4, said moieties containing a 5-membered imide ring being thecondensation product of 1 mol of tetracarboxylic acid anhydride and 2mols of primary aromatic amino carboxylic acid.
 6. A lacquer accordingto claim 4, said moieties containing a 5-membered imide ring being thecondensation product of 1 mol of tetracarboxylic acid anhydride and 2mols of primary aromatic amino alcohol.